reducing prop slip
 

i keep running the number through the slip calc and wind up around 25% slip. How can i redcue taht? i tried out a mirage 3 blade (not a plus) and could only get about 62-63 at 5400.

Would a 4 or more blade prop hookup more? Currently my drive won't trim up as high as it should (still figuring that one out). But even with the old engien/drive it always had high slip #s.

It does have a through hull fitting about 5'-6' from the transon. Older Scarabs are the only performance boats i've ever seen with these kind of through hull. Quite frankly they look like they belong on cruisers. Is it possible this is could be causing a wierd flow of water on the running surfaces? Like as in perhaps the water coming to the prop isn't so clean and full or air bubbles hence any props i've tried don't hook up so well??

What boat do you have? Those mirages slip like crazy on larger boats. Switching to 4 blades will make a big difference.

What percentage of slip should you have? I'm getting around 22-25% too (if trs drives have a 1.5 ratio). I also have through hull fittings if that could be causing the problem.

1987 27' scarab bravo with 1.5 gears. i also have a nosecone on the drive.

I get around 11% with my Bravo 1.Are you using a GPS speedo?Does the trim work enough to get the bow out of the water?Bob

the bow seems a little low due to the trim issues we'll see late ron today.

th speed was on GPS. I didn;t reset teh trip settings so ididnt; get the ctuall max speed. My buddy was watching it though whie i was driving.

I feel your pain my brother, know matter waht I do I can't gain any speed put on an Imco 2" shortie gained some rpm no speed this piece of crap doesn't care if I have 1 pass. with a 1/2 tank or 2 pass. with a full tank it won't go above 66 mph on gps that's not true I went up 1/10 mph my barge is an 88 28'` excel. It's weird I'll hit a certain speed maybe 55-60 and it almost feels like I hit something in the water but what I think is happening is the the boat is rising higher out of the water and then starts to nose dive. I'm wondering if an extension box would help to offset some more weight either that or have my fat sister sit on the swim platform but then I might not be able to plane off.

ok fully trimmed she ran like 62-63. The slip #s are damn near 30% ????

ideas????

gotta be the prop try some hydro's they love my non step fountain,

Puder, try a Mercury Revolution, should be worth 2-3 MPH

I get 17 % with my boat at 77 mph. And I am thinking about adding stand off boxes this winter.

well ladies i got my greedy little hands on some 5 blade herrings to try out :D

i think they might be a little to big though . BUT we'll see if they bite any better than the mirages. I'm thinking they should. FYI the difference in quality between them and a merc prop seeems to be night and day. The blades are super thin and sharp as hell.

You may want to try a Mirage+ they have more cup and bite a lot better than a Mirage. Or send your props out to have some cup added. One propr shop told me that is why Merc came out with the Mirage+, because all the shops were cupping the Mirage.

A Hydromotive will give you more transome lift. Some boats , like Fountains, like that others don't.
I'm seeing 400 rpm drop from a Mirage 25 to a Mirage+25 and 10% slip on a 34' Super Hawaii. That's a 32' running surface with a nothched transom and 9000lbs running.

wel i tried a lefty 29p 5 blade herring. WAY better.
i picked up 1 mph BUT it was at a MUCH lower rpm. The wheel is too big the slip numbers came down some which is good.

63mph at 4300 rpms isn't too bad. I need to get it up into the 5300-5500rpm range though.

puder what motor do you have, Today was a banner day for me I took off the grate on my thru hull water intake was running a 24p Bravo 1-4 blade at 5200 and for the first time got 70.4 on gps out of the old pig.

ho, very nice!

my engine is basilcally a 525sc. Very similar setup I have a little more cam than the merc setup and my static compresison is a tad higher. She made 551hp at 5400.

what model do you have it sounds like we're comparable in HP mine is a 88 28' excel I put an Imco 2" shortie on and was running slower than the stock unit took off that cover for the south bay strainer and I guess lost some drag, different direction was like a mph slower but who cares it's close enough for me I 'm going to try a 25 mirage plus then send my best one to houston prop, but like a moron I sold a mint 25 last year cause I couldn't spin it on the other scow.

I just noted all my rpms/mph readings in 500 rpm increments this past weekend. I only had 7% slip at 5100rpm. Running 25" Hydros. Going to put 26" on for this weekend and see if I can squeeze out another 2-3 mph.

Any decent motor is going to stop making torque and start building hp at 5252 rpm so I would expect more slippage past 5200 rpm. Does it follow logic to try and prop the boat a little larger to max out rpms at 5200 or would it make sense to go with a smaller prop and spin it up faster?

homan so teh shorty lower made you loose speed?
removing the whack crauiser style through hullpickup gained speed???

my boat is a 1987 26' scarab excel I think its pretty much the same hull as the 28 excel but without a swim platform. FYI i measured it once and i got 27' so i call it a 27' (ya gotta squeeze in that extra foot!!!!)

shes running well with the lefty 29 5 blade. solid 63 at 4300 rpms. On ceth rpms come up to teh powwer band she shdoul crank. Hering is willing to trade me props to getoteh right rpm range.

I refiguerd my slip number and i am down to 20%

87 26' I had the same boat just sold it in July had a 502 mag. built to hp 500 pretty much, merlin heads 10:1 comp. 850 dbl. pump, roller valve train gil dry pipes w/pump crossover pipe. That one went 67 gps with a Mirage 23 @4800 but I had a 1:36 bravo 1 upper, that I found out after I sold it. I'm by no means a supreme motor head but alot of people say Oh you gotta rev 5600 to get the power which means pitching down, I say why not spin 5200 and save the motor a bit. But the 4300 is too low it's like driving around 3 500lb passengers, it's a big load on the motor. How do you like the windshield for me it was annoying as hell. Also did you have that little spoiler on the back e-mail me a pict. if you have one. [email protected]

yeah at 4300 my blower is making 7 psi of boost. TOO MUCH!!! With the smaller prop and 5400 rpms it was making 5psi and 62 mph.

i lieketh windshield. It sucked withet odl interior BUT i biult anew dash, dash panel, and put drop down bolsters in. SO its not bad the windshield kicks up the winds so when you're sitting in the drop down the wind isn;t too bad and when your standing you get hit with it anyway.

spoiler??? I have a stainless rail on the back if thats what your reffering to. My boat origonally had an alpha/ 330 setup with 1.32 gears. Never did run worth a damn with that setup and every time I took it out i felt like i was about to pop the drive.

nice, that's one thing I couldn't understand why they put those dopey aluminumbases for the seats instead of standups, as far as the spoiler it was about 5" high and looked like the ones on the back of an 82 trans am. My side airscoops were puke yellow I painted them hi flake metallic silver and black. What were the air blowers on the bow supposed to be for. With a blower you sound like you should have more power and speed than mine did

definatly dont; have the transam wing. If i did it would have been sawzalled off long ago. I amthignking abtou havign eth side panels removed and glassing the holes over and puting in naca vents ove rteh winter. Should update the look a little.

as for power, 550hp. Shes just a lil huffer moter :D

Are you using a digital GPS? I have noticed great variations in the accuracy of analog vs digital. Whenever I tune it is always with digital GPS and Digital GPS Speedo. The best I get is 16% slip. That is on a light daytona cat w/ bravo type drive and lab props. I have tried x-boxes, nose cones and various engine heighgts. I question anyones accuracy to get better unless it is a race boat or professionally dialed in pleasure boat, i.e., Skater.

i am using a garmin gps76 non mapping.

Sorry, I meant Digital Tach.

tach is a gaffrig with hour meter hooked up to eth gray wire of an MSD box

16% slip with extreme "V" hulls like ours??!!?? That's not bad at all. Anyone doing much better either has faulty measuring equipment or is VERY optimistic. --- Jer

Now, Cat's aired out WILL get those #'s down some. --- Jer

us1 7% really that is unbelievable. what fountain is that? size yr?